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package java.io;

import java.util.Objects;


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 < 0} implies the buffer is empty,
     * {@code in == out} 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} so
     * that it is connected to the piped writer
     * {@code src}. Data written to {@code src}
     * will then be available as input from this stream.
     *
     * @param      src   the stream to connect to.
     * @throws     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} so that it is connected
     * to the piped writer {@code src} and uses the specified
     * pipe size for the pipe's buffer. Data written to {@code src}
     * 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.
     * @throws     IOException  if an I/O error occurs.
     * @throws     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} 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}
     * 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} 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}
     * before being used.
     *
     * @param   pipeSize the size of the pipe's buffer.
     * @throws  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}.
     * If this object is already connected to some
     * other piped writer, an {@code IOException}
     * is thrown.
     * <p>
     * If {@code src} is an
     * unconnected piped writer and {@code snk}
     * is an unconnected piped reader, they
     * may be connected by either the call:
     *
     * <pre>{@code snk.connect(src)} </pre>
     * <p>
     * or the call:
     *
     * <pre>{@code src.connect(snk)} </pre>
     * <p>
     * The two calls have the same effect.
     *
     * @param      src   The piped writer to connect to.
     * @throws     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} 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} if the end of the
     *          stream is reached.
     * @throws  IOException  if the pipe is
     *          <a href=PipedInputStream.html#BROKEN> {@code broken}</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;
    }

    
{@inheritDoc}

 Fewer than len characters will be read if len exceeds the pipe's buffer size. 
Params:
  • cbuf –  {@inheritDoc}
  • off –   {@inheritDoc}
  • len –   {@inheritDoc}
Throws:
Returns:    {@inheritDoc}
/**
     * {@inheritDoc}
     *
     * <p> Fewer than {@code len} characters will be read if
     * {@code len} exceeds the pipe's buffer size.
     *
     * @param      cbuf  {@inheritDoc}
     * @param      off   {@inheritDoc}
     * @param      len   {@inheritDoc}
     *
     * @return     {@inheritDoc}
     *
     * @throws     IndexOutOfBoundsException {@inheritDoc}
     * @throws     IOException  if the pipe is
     *             <a href=PipedInputStream.html#BROKEN> {@code broken}</a>,
     *             {@link #connect(java.io.PipedWriter) unconnected}, closed,
     *             or an I/O error occurs.
     */
    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");
        }

        Objects.checkFromIndexSize(off, len, cbuf.length);
        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.
     *
     * @throws     IOException  if the pipe is
     *             <a href=PipedInputStream.html#BROKEN> {@code broken}</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.
     *
     * @throws     IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
        in = -1;
        closedByReader = true;
    }
}