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package java.io;

import java.io.*;


A piped output stream can be connected to a piped input stream to create a communications pipe. The piped output stream is the sending end of the pipe. Typically, data is written to a PipedOutputStream object by one thread and data is read from the connected PipedInputStream by some other thread. Attempting to use both objects from a single thread is not recommended as it may deadlock the thread. The pipe is said to be  broken  if a
thread that was reading data bytes from the connected piped input
stream is no longer alive.

Author: James Gosling
See Also:
Since:  1.0
/**
 * A piped output stream can be connected to a piped input stream
 * to create a communications pipe. The piped output stream is the
 * sending end of the pipe. Typically, data is written to a
 * {@code PipedOutputStream} object by one thread and data is
 * read from the connected {@code PipedInputStream} by some
 * other thread. Attempting to use both objects from a single thread
 * is not recommended as it may deadlock the thread.
 * The pipe is said to be <a id=BROKEN> <i>broken</i> </a> if a
 * thread that was reading data bytes from the connected piped input
 * stream is no longer alive.
 *
 * @author  James Gosling
 * @see     java.io.PipedInputStream
 * @since   1.0
 */
public class PipedOutputStream extends OutputStream {

        /* 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). */
    private PipedInputStream sink;

    
Creates a piped output stream connected to the specified piped input stream. Data bytes written to this stream will then be available as input from snk. 
Params:
  • snk –   The piped input stream to connect to.
Throws:
/**
     * Creates a piped output stream connected to the specified piped
     * input stream. Data bytes written to this stream will then be
     * available as input from {@code snk}.
     *
     * @param      snk   The piped input stream to connect to.
     * @throws     IOException  if an I/O error occurs.
     */
    public PipedOutputStream(PipedInputStream snk)  throws IOException {
        connect(snk);
    }

    
Creates a piped output stream that is not yet connected to a
piped input stream. It must be connected to a piped input stream,
either by the receiver or the sender, before being used.

See Also:
/**
     * Creates a piped output stream that is not yet connected to a
     * piped input stream. It must be connected to a piped input stream,
     * either by the receiver or the sender, before being used.
     *
     * @see     java.io.PipedInputStream#connect(java.io.PipedOutputStream)
     * @see     java.io.PipedOutputStream#connect(java.io.PipedInputStream)
     */
    public PipedOutputStream() {
    }

    
Connects this piped output stream to a receiver. If this object is already connected to some other piped input stream, an IOException is thrown. 
 If snk is an unconnected piped input stream and src is an unconnected piped output stream, they may be connected by either the call: 
src.connect(snk)

or the call:

snk.connect(src)

The two calls have the same effect.

Params:
  • snk –   the piped input stream to connect to.
Throws:
/**
     * Connects this piped output stream to a receiver. If this object
     * is already connected to some other piped input stream, an
     * {@code IOException} is thrown.
     * <p>
     * If {@code snk} is an unconnected piped input stream and
     * {@code src} is an unconnected piped output stream, they may
     * be connected by either the call:
     * <blockquote><pre>
     * src.connect(snk)</pre></blockquote>
     * or the call:
     * <blockquote><pre>
     * snk.connect(src)</pre></blockquote>
     * The two calls have the same effect.
     *
     * @param      snk   the piped input stream to connect to.
     * @throws     IOException  if an I/O error occurs.
     */
    public synchronized void connect(PipedInputStream snk) throws IOException {
        if (snk == null) {
            throw new NullPointerException();
        } else if (sink != null || snk.connected) {
            throw new IOException("Already connected");
        }
        sink = snk;
        snk.in = -1;
        snk.out = 0;
        snk.connected = true;
    }

    
Writes the specified byte to the piped output stream. 
 Implements the write method of OutputStream. 
Params:
  • b –  the byte to be written.
Throws:
/**
     * Writes the specified {@code byte} to the piped output stream.
     * <p>
     * Implements the {@code write} method of {@code OutputStream}.
     *
     * @param   b   the {@code byte} to be written.
     * @throws  IOException if the pipe is <a href=#BROKEN> broken</a>,
     *          {@link #connect(java.io.PipedInputStream) unconnected},
     *          closed, or if an I/O error occurs.
     */
    public void write(int b)  throws IOException {
        if (sink == null) {
            throw new IOException("Pipe not connected");
        }
        sink.receive(b);
    }

    
Writes len bytes from the specified byte array starting at offset off to this piped output stream. This method blocks until all the bytes are written to the output stream. 
Params:
  • b –     the data.
  • off –   the start offset in the data.
  • len –   the number of bytes to write.
Throws:
/**
     * Writes {@code len} bytes from the specified byte array
     * starting at offset {@code off} to this piped output stream.
     * This method blocks until all the bytes are written to the output
     * stream.
     *
     * @param   b     the data.
     * @param   off   the start offset in the data.
     * @param   len   the number of bytes to write.
     * @throws  IOException if the pipe is <a href=#BROKEN> broken</a>,
     *          {@link #connect(java.io.PipedInputStream) unconnected},
     *          closed, or if an I/O error occurs.
     */
    public void write(byte b[], int off, int len) throws IOException {
        if (sink == null) {
            throw new IOException("Pipe not connected");
        } else if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) ||
                   ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }
        sink.receive(b, off, len);
    }

    
Flushes this output stream and forces any buffered output bytes
to be written out.
This will notify any readers that bytes are waiting in the pipe.

Throws:
  • IOException – if an I/O error occurs.
/**
     * Flushes this output stream and forces any buffered output bytes
     * to be written out.
     * This will notify any readers that bytes are waiting in the pipe.
     *
     * @throws    IOException if an I/O error occurs.
     */
    public synchronized void flush() throws IOException {
        if (sink != null) {
            synchronized (sink) {
                sink.notifyAll();
            }
        }
    }

    
Closes this piped output stream and releases any system resources
associated with this stream. This stream may no longer be used for
writing bytes.

Throws:
  • IOException –  if an I/O error occurs.
/**
     * Closes this piped output stream and releases any system resources
     * associated with this stream. This stream may no longer be used for
     * writing bytes.
     *
     * @throws     IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
        if (sink != null) {
            sink.receivedLast();
        }
    }
}