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package java.io;



Piped character-input streams.

Author:     Mark Reinhold
Since:      1.1
/**
 * Piped character-input streams.
 *
 * @author      Mark Reinhold
 * @since       1.1
 */

public class PipedReader extends Reader {
    boolean closedByWriter = false;
    boolean closedByReader = false;
    boolean connected = false;

    /* REMIND: identification of the read and write sides needs to be
       more sophisticated.  Either using thread groups (but what about
       pipes within a thread?) or using finalization (but it may be a
       long time until the next GC). */
    Thread readSide;
    Thread writeSide;

   
The size of the pipe's circular input buffer.

/**
    * The size of the pipe's circular input buffer.
    */
    private static final int DEFAULT_PIPE_SIZE = 1024;

    
The circular buffer into which incoming data is placed.

/**
     * The circular buffer into which incoming data is placed.
     */
    char buffer[];

    
The index of the position in the circular buffer at which the
next character of data will be stored when received from the connected
piped writer. in<0 implies the buffer is empty,
in==out implies the buffer is full

/**
     * The index of the position in the circular buffer at which the
     * next character of data will be stored when received from the connected
     * piped writer. <code>in&lt;0</code> implies the buffer is empty,
     * <code>in==out</code> implies the buffer is full
     */
    int in = -1;

    
The index of the position in the circular buffer at which the next
character of data will be read by this piped reader.

/**
     * The index of the position in the circular buffer at which the next
     * character of data will be read by this piped reader.
     */
    int out = 0;

    
Creates a PipedReader so
that it is connected to the piped writer
src. Data written to src
will then be available as input from this stream.

Params:
  • src –   the stream to connect to.
Throws:
/**
     * Creates a <code>PipedReader</code> so
     * that it is connected to the piped writer
     * <code>src</code>. Data written to <code>src</code>
     * will then be available as input from this stream.
     *
     * @param      src   the stream to connect to.
     * @exception  IOException  if an I/O error occurs.
     */
    public PipedReader(PipedWriter src) throws IOException {
        this(src, DEFAULT_PIPE_SIZE);
    }

    
Creates a PipedReader so that it is connected
to the piped writer src and uses the specified
pipe size for the pipe's buffer. Data written to src
will then be  available as input from this stream.

Params:
  • src –       the stream to connect to.
  • pipeSize –  the size of the pipe's buffer.
Throws:
Since:     1.6
/**
     * Creates a <code>PipedReader</code> so that it is connected
     * to the piped writer <code>src</code> and uses the specified
     * pipe size for the pipe's buffer. Data written to <code>src</code>
     * will then be  available as input from this stream.

     * @param      src       the stream to connect to.
     * @param      pipeSize  the size of the pipe's buffer.
     * @exception  IOException  if an I/O error occurs.
     * @exception  IllegalArgumentException if {@code pipeSize <= 0}.
     * @since      1.6
     */
    public PipedReader(PipedWriter src, int pipeSize) throws IOException {
        initPipe(pipeSize);
        connect(src);
    }


    
Creates a PipedReader so that it is not yet 
connected. It must be connected to a PipedWriter
before being used.

/**
     * Creates a <code>PipedReader</code> so
     * that it is not yet {@linkplain #connect(java.io.PipedWriter)
     * connected}. It must be {@linkplain java.io.PipedWriter#connect(
     * java.io.PipedReader) connected} to a <code>PipedWriter</code>
     * before being used.
     */
    public PipedReader() {
        initPipe(DEFAULT_PIPE_SIZE);
    }

    
Creates a PipedReader so that it is not yet connected and uses the specified pipe size for the pipe's buffer. It must be connected to a PipedWriter
before being used.

Params:
  • pipeSize – the size of the pipe's buffer.
Throws:
Since:     1.6
/**
     * Creates a <code>PipedReader</code> so that it is not yet
     * {@link #connect(java.io.PipedWriter) connected} and uses
     * the specified pipe size for the pipe's buffer.
     * It must be  {@linkplain java.io.PipedWriter#connect(
     * java.io.PipedReader) connected} to a <code>PipedWriter</code>
     * before being used.
     *
     * @param   pipeSize the size of the pipe's buffer.
     * @exception  IllegalArgumentException if {@code pipeSize <= 0}.
     * @since      1.6
     */
    public PipedReader(int pipeSize) {
        initPipe(pipeSize);
    }

    private void initPipe(int pipeSize) {
        if (pipeSize <= 0) {
            throw new IllegalArgumentException("Pipe size <= 0");
        }
        buffer = new char[pipeSize];
    }

    
Causes this piped reader to be connected
to the piped  writer src.
If this object is already connected to some
other piped writer, an IOException
is thrown.


If src is an
unconnected piped writer and snk
is an unconnected piped reader, they
may be connected by either the call:

snk.connect(src) 



or the call:

src.connect(snk) 



The two calls have the same effect.

Params:
  • src –   The piped writer to connect to.
Throws:
/**
     * Causes this piped reader to be connected
     * to the piped  writer <code>src</code>.
     * If this object is already connected to some
     * other piped writer, an <code>IOException</code>
     * is thrown.
     * <p>
     * If <code>src</code> is an
     * unconnected piped writer and <code>snk</code>
     * is an unconnected piped reader, they
     * may be connected by either the call:
     *
     * <pre><code>snk.connect(src)</code> </pre>
     * <p>
     * or the call:
     *
     * <pre><code>src.connect(snk)</code> </pre>
     * <p>
     * The two calls have the same effect.
     *
     * @param      src   The piped writer to connect to.
     * @exception  IOException  if an I/O error occurs.
     */
    public void connect(PipedWriter src) throws IOException {
        src.connect(this);
    }

    
Receives a char of data. This method will block if no input is
available.

/**
     * Receives a char of data. This method will block if no input is
     * available.
     */
    synchronized void receive(int c) throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByWriter || closedByReader) {
            throw new IOException("Pipe closed");
        } else if (readSide != null && !readSide.isAlive()) {
            throw new IOException("Read end dead");
        }

        writeSide = Thread.currentThread();
        while (in == out) {
            if ((readSide != null) && !readSide.isAlive()) {
                throw new IOException("Pipe broken");
            }
            /* full: kick any waiting readers */
            notifyAll();
            try {
                wait(1000);
            } catch (InterruptedException ex) {
                throw new java.io.InterruptedIOException();
            }
        }
        if (in < 0) {
            in = 0;
            out = 0;
        }
        buffer[in++] = (char) c;
        if (in >= buffer.length) {
            in = 0;
        }
    }

    
Receives data into an array of characters.  This method will
block until some input is available.

/**
     * Receives data into an array of characters.  This method will
     * block until some input is available.
     */
    synchronized void receive(char c[], int off, int len)  throws IOException {
        while (--len >= 0) {
            receive(c[off++]);
        }
    }

    
Notifies all waiting threads that the last character of data has been
received.

/**
     * Notifies all waiting threads that the last character of data has been
     * received.
     */
    synchronized void receivedLast() {
        closedByWriter = true;
        notifyAll();
    }

    
Reads the next character of data from this piped stream.
If no character is available because the end of the stream
has been reached, the value -1 is returned.
This method blocks until input data is available, the end of
the stream is detected, or an exception is thrown.

Throws:
Returns:    the next character of data, or -1 if the end of the
            stream is reached.
/**
     * Reads the next character of data from this piped stream.
     * If no character is available because the end of the stream
     * has been reached, the value <code>-1</code> is returned.
     * This method blocks until input data is available, the end of
     * the stream is detected, or an exception is thrown.
     *
     * @return     the next character of data, or <code>-1</code> if the end of the
     *             stream is reached.
     * @exception  IOException  if the pipe is
     *          <a href=PipedInputStream.html#BROKEN> <code>broken</code></a>,
     *          {@link #connect(java.io.PipedWriter) unconnected}, closed,
     *          or an I/O error occurs.
     */
    public synchronized int read()  throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
            throw new IOException("Pipe closed");
        } else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }

        readSide = Thread.currentThread();
        int trials = 2;
        while (in < 0) {
            if (closedByWriter) {
                /* closed by writer, return EOF */
                return -1;
            }
            if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < 0)) {
                throw new IOException("Pipe broken");
            }
            /* might be a writer waiting */
            notifyAll();
            try {
                wait(1000);
            } catch (InterruptedException ex) {
                throw new java.io.InterruptedIOException();
            }
        }
        int ret = buffer[out++];
        if (out >= buffer.length) {
            out = 0;
        }
        if (in == out) {
            /* now empty */
            in = -1;
        }
        return ret;
    }

    
Reads up to len characters of data from this piped
stream into an array of characters. Less than len characters
will be read if the end of the data stream is reached or if
len exceeds the pipe's buffer size. This method
blocks until at least one character of input is available.

Params:
  • cbuf –     the buffer into which the data is read.
  • off –   the start offset of the data.
  • len –   the maximum number of characters read.
Throws:
Returns:    the total number of characters read into the buffer, or
            -1 if there is no more data because the end of
            the stream has been reached.
/**
     * Reads up to <code>len</code> characters of data from this piped
     * stream into an array of characters. Less than <code>len</code> characters
     * will be read if the end of the data stream is reached or if
     * <code>len</code> exceeds the pipe's buffer size. This method
     * blocks until at least one character of input is available.
     *
     * @param      cbuf     the buffer into which the data is read.
     * @param      off   the start offset of the data.
     * @param      len   the maximum number of characters read.
     * @return     the total number of characters read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the stream has been reached.
     * @exception  IOException  if the pipe is
     *                  <a href=PipedInputStream.html#BROKEN> <code>broken</code></a>,
     *                  {@link #connect(java.io.PipedWriter) unconnected}, closed,
     *                  or an I/O error occurs.
     * @exception  IndexOutOfBoundsException {@inheritDoc}
     */
    public synchronized int read(char cbuf[], int off, int len)  throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
            throw new IOException("Pipe closed");
        } else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }

        if ((off < 0) || (off > cbuf.length) || (len < 0) ||
            ((off + len) > cbuf.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }

        /* possibly wait on the first character */
        int c = read();
        if (c < 0) {
            return -1;
        }
        cbuf[off] =  (char)c;
        int rlen = 1;
        while ((in >= 0) && (--len > 0)) {
            cbuf[off + rlen] = buffer[out++];
            rlen++;
            if (out >= buffer.length) {
                out = 0;
            }
            if (in == out) {
                /* now empty */
                in = -1;
            }
        }
        return rlen;
    }

    
Tell whether this stream is ready to be read.  A piped character
stream is ready if the circular buffer is not empty.

Throws:
/**
     * Tell whether this stream is ready to be read.  A piped character
     * stream is ready if the circular buffer is not empty.
     *
     * @exception  IOException  if the pipe is
     *                  <a href=PipedInputStream.html#BROKEN> <code>broken</code></a>,
     *                  {@link #connect(java.io.PipedWriter) unconnected}, or closed.
     */
    public synchronized boolean ready() throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
            throw new IOException("Pipe closed");
        } else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }
        if (in < 0) {
            return false;
        } else {
            return true;
        }
    }

    
Closes this piped stream and releases any system resources
associated with the stream.

Throws:
  • IOException –  if an I/O error occurs.
/**
     * Closes this piped stream and releases any system resources
     * associated with the stream.
     *
     * @exception  IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
        in = -1;
        closedByReader = true;
    }
}