362 lines
11 KiB
Java
362 lines
11 KiB
Java
/* PipedReader.java -- Read portion of piped character streams.
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Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.io;
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// NOTE: This implementation is very similar to that of PipedInputStream.
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// If you fix a bug in here, chances are you should make a similar change to
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// the PipedInputStream code.
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/**
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* An input stream that reads characters from a piped writer to which it is
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* connected.
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* <p>
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* Data is read and written to an internal buffer. It is highly recommended
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* that the <code>PipedReader</code> and connected <code>PipedWriter</code>
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* be part of different threads. If they are not, there is a possibility
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* that the read and write operations could deadlock their thread.
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*
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* @specnote The JDK implementation appears to have some undocumented
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* functionality where it keeps track of what thread is writing
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* to pipe and throws an IOException if that thread susequently
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* dies. This behaviour seems dubious and unreliable - we don't
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* implement it.
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*
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* @author Aaron M. Renn (arenn@urbanophile.com)
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*/
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public class PipedReader extends Reader
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{
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/** PipedWriter to which this is connected. Null only if this
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* Reader hasn't been connected yet. */
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PipedWriter source;
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/** Set to true if close() has been called on this Reader. */
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boolean closed;
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/**
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* The size of the internal buffer used for input/output.
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*/
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static final int PIPE_SIZE = 2048;
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/**
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* This is the internal circular buffer used for storing chars written
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* to the pipe and from which chars are read by this stream
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*/
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char[] buffer = new char[PIPE_SIZE];
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/**
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* The index into buffer where the next char from the connected
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* <code>PipedWriter</code> will be written. If this variable is
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* equal to <code>out</code>, then the buffer is full. If set to < 0,
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* the buffer is empty.
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*/
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int in = -1;
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/**
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* This index into the buffer where chars will be read from.
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*/
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int out = 0;
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/** Buffer used to implement single-argument read/receive */
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char[] read_buf = new char[1];
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/**
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* Creates a new <code>PipedReader</code> that is not connected to a
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* <code>PipedWriter</code>. It must be connected before chars can
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* be read from this stream.
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*/
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public PipedReader()
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{
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}
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/**
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* This constructor creates a new <code>PipedReader</code> and connects
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* it to the passed in <code>PipedWriter</code>. The stream is then
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* ready for reading.
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*
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* @param source The <code>PipedWriter</code> to connect this stream to
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*
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* @exception IOException If <code>source</code> is already connected.
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*/
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public PipedReader(PipedWriter source) throws IOException
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{
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connect(source);
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}
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/**
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* This method connects this stream to the passed in
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* <code>PipedWriter</code>.
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* This stream is then ready for reading. If this stream is already
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* connected or has been previously closed, then an exception is thrown
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*
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* @param source The <code>PipedWriter</code> to connect this stream to
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*
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* @exception IOException If this PipedReader or <code>source</code>
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* has been connected already.
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*/
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public void connect(PipedWriter source) throws IOException
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{
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// The JDK (1.3) does not appear to check for a previously closed
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// connection here.
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if (this.source != null || source.sink != null)
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throw new IOException ("Already connected");
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source.sink = this;
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this.source = source;
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}
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/**
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* This method is used by the connected <code>PipedWriter</code> to
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* write chars into the buffer.
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*
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* @param buf The array containing chars to write to this stream
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* @param offset The offset into the array to start writing from
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* @param len The number of chars to write.
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*
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* @exception IOException If an error occurs
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* @specnote This code should be in PipedWriter.write, but we
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* put it here in order to support that bizarre recieve(int)
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* method.
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*/
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void receive(char[] buf, int offset, int len)
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throws IOException
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{
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synchronized (lock)
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{
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if (closed)
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throw new IOException ("Pipe closed");
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int bufpos = offset;
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int copylen;
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while (len > 0)
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{
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try
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{
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while (in == out)
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{
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// The pipe is full. Wake up any readers and wait for them.
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lock.notifyAll();
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lock.wait();
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// The pipe could have been closed while we were waiting.
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if (closed)
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throw new IOException ("Pipe closed");
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}
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}
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catch (InterruptedException ix)
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{
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throw new InterruptedIOException ();
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}
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if (in < 0) // The pipe is empty.
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in = 0;
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// Figure out how many chars from buf can be copied without
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// overrunning out or going past the length of the buffer.
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if (in < out)
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copylen = Math.min (len, out - in);
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else
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copylen = Math.min (len, buffer.length - in);
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// Copy chars until the pipe is filled, wrapping if necessary.
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System.arraycopy(buf, bufpos, buffer, in, copylen);
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len -= copylen;
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bufpos += copylen;
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in += copylen;
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if (in == buffer.length)
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in = 0;
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}
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// Notify readers that new data is in the pipe.
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lock.notifyAll();
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}
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}
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/**
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* This method reads chars from the stream into a caller supplied buffer.
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* It starts storing chars at position <code>offset</code> into the
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* buffer and
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* reads a maximum of <code>len</code> chars. Note that this method
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* can actually
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* read fewer than <code>len</code> chars. The actual number of chars
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* read is
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* returned. A -1 is returned to indicated that no chars can be read
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* because the end of the stream was reached. If the stream is already
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* closed, a -1 will again be returned to indicate the end of the stream.
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* <p>
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* This method will block if no char is available to be read.
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*/
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public int read() throws IOException
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{
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// Method operates by calling the multichar overloaded read method
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// Note that read_buf is an internal instance variable. I allocate it
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// there to avoid constant reallocation overhead for applications that
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// call this method in a loop at the cost of some unneeded overhead
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// if this method is never called.
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int r = read(read_buf, 0, 1);
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return r != -1 ? read_buf[0] : -1;
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}
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/**
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* This method reads characters from the stream into a caller supplied
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* buffer. It starts storing chars at position <code>offset</code> into
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* the buffer and reads a maximum of <code>len</code> chars. Note that
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* this method can actually read fewer than <code>len</code> chars.
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* The actual number of chars read is
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* returned. A -1 is returned to indicated that no chars can be read
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* because the end of the stream was reached - ie close() was called on the
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* connected PipedWriter.
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* <p>
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* This method will block if no chars are available to be read.
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*
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* @param buf The buffer into which chars will be stored
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* @param offset The index into the buffer at which to start writing.
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* @param len The maximum number of chars to read.
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*
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* @exception IOException If <code>close()</code> was called on this Piped
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* Reader.
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*/
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public int read(char[] buf, int offset, int len)
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throws IOException
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{
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synchronized (lock)
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{
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if (source == null)
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throw new IOException ("Not connected");
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if (closed)
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throw new IOException ("Pipe closed");
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// If the buffer is empty, wait until there is something in the pipe
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// to read.
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try
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{
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while (in < 0)
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{
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if (source.closed)
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return -1;
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lock.wait();
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}
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}
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catch (InterruptedException ix)
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{
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throw new InterruptedIOException();
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}
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int total = 0;
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int copylen;
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while (true)
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{
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// Figure out how many chars from the pipe can be copied without
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// overrunning in or going past the length of buf.
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if (out < in)
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copylen = Math.min (len, in - out);
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else
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copylen = Math.min (len, buffer.length - out);
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System.arraycopy (buffer, out, buf, offset, copylen);
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offset += copylen;
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len -= copylen;
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out += copylen;
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total += copylen;
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if (out == buffer.length)
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out = 0;
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if (out == in)
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{
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// Pipe is now empty.
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in = -1;
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out = 0;
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}
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// If output buffer is filled or the pipe is empty, we're done.
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if (len == 0 || in == -1)
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{
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// Notify any waiting Writer that there is now space
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// to write.
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lock.notifyAll();
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return total;
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}
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}
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}
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}
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public boolean ready() throws IOException
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{
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// The JDK 1.3 implementation does not appear to check for the closed or
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// unconnected stream conditions here. However, checking for a
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// closed stream is explicitly required by the JDK 1.2 and 1.3
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// documentation (for Reader.close()), so we do it.
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synchronized (lock)
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{
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if (closed)
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throw new IOException("Pipe closed");
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if (in < 0)
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return false;
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int count;
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if (out < in)
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count = in - out;
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else
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count = (buffer.length - out) - in;
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return (count > 0);
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}
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}
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/**
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* This methods closes the stream so that no more data can be read
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* from it.
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*
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* @exception IOException If an error occurs
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*/
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public void close() throws IOException
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{
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synchronized (lock)
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{
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closed = true;
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// Wake any thread which may be in receive() waiting to write data.
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lock.notifyAll();
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}
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}
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}
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