src/java.base/share/classes/java/io/PipedInputStream.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * accompanied this code).
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package java.io;

import java.util.Objects;

/**
 * A piped input stream should be connected
 * to a piped output stream; the piped  input
 * stream then provides whatever data bytes
 * are written to the piped output  stream.
 * Typically, data is read from a {@code PipedInputStream}
 * object by one thread  and data is written
 * to the corresponding {@code PipedOutputStream}
 * by some  other thread. Attempting to use
 * both objects from a single thread is not
 * recommended, as it may deadlock the thread.
 * The piped input stream contains a buffer,
 * decoupling read operations from write operations,
 * within limits.
 * A pipe is said to be <a id="BROKEN"> <i>broken</i> </a> if a
 * thread that was providing data bytes to the connected
 * piped output stream is no longer alive.
 *
 * @author  James Gosling
 * @see     java.io.PipedOutputStream
 * @since   1.0
 */
public class PipedInputStream extends InputStream {
    boolean closedByWriter;
    volatile boolean closedByReader;
    boolean connected;

        /* 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;

    private static final int DEFAULT_PIPE_SIZE = 1024;

    /**
     * The default size of the pipe's circular input buffer.
     * @since   1.1
     */
    // This used to be a constant before the pipe size was allowed
    // to change. This field will continue to be maintained
    // for backward compatibility.
    protected static final int PIPE_SIZE = DEFAULT_PIPE_SIZE;

    /**
     * The circular buffer into which incoming data is placed.
     * @since   1.1
     */
    protected byte buffer[];

    /**
     * The index of the position in the circular buffer at which the
     * next byte of data will be stored when received from the connected
     * piped output stream. {@code in < 0} implies the buffer is empty,
     * {@code in == out} implies the buffer is full
     * @since   1.1
     */
    protected int in = -1;

    /**
     * The index of the position in the circular buffer at which the next
     * byte of data will be read by this piped input stream.
     * @since   1.1
     */
    protected int out = 0;

    /**
     * Creates a {@code PipedInputStream} so
     * that it is connected to the piped output
     * stream {@code src}. Data bytes 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 PipedInputStream(PipedOutputStream src) throws IOException {
        this(src, DEFAULT_PIPE_SIZE);
    }

    /**
     * Creates a {@code PipedInputStream} so that it is
     * connected to the piped output stream
     * {@code src} and uses the specified pipe size for
     * the pipe's buffer.
     * Data bytes 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
     */
    @SuppressWarnings("this-escape")
    public PipedInputStream(PipedOutputStream src, int pipeSize)
            throws IOException {
         initPipe(pipeSize);
         connect(src);
    }

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

    /**
     * Creates a {@code PipedInputStream} so that it is not yet
     * {@linkplain #connect(java.io.PipedOutputStream) connected} and
     * uses the specified pipe size for the pipe's buffer.
     * It must be {@linkplain java.io.PipedOutputStream#connect(
     * java.io.PipedInputStream)
     * connected} to a {@code PipedOutputStream} before being used.
     *
     * @param      pipeSize the size of the pipe's buffer.
     * @throws     IllegalArgumentException if {@code pipeSize <= 0}.
     * @since      1.6
     */
    public PipedInputStream(int pipeSize) {
        initPipe(pipeSize);
    }

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

    /**
     * Causes this piped input stream to be connected
     * to the piped  output stream {@code src}.
     * If this object is already connected to some
     * other piped output  stream, an {@code IOException}
     * is thrown.
     * <p>
     * If {@code src} is an
     * unconnected piped output stream and {@code snk}
     * is an unconnected piped input stream, they
     * may be connected by either the call:
     *
     * {@snippet lang=java :
     *     snk.connect(src)
     * }
     * <p>
     * or the call:
     *
     * {@snippet lang=java :
     *     src.connect(snk)
     * }
     * <p>
     * The two calls have the same effect.
     *
     * @param      src   The piped output stream to connect to.
     * @throws     IOException  if an I/O error occurs.
     */
    public void connect(PipedOutputStream src) throws IOException {
        src.connect(this);
    }

    /**
     * Receives a byte of data.  This method will block if no input is
     * available.
     * @param   b the byte being received
     * @throws  IOException If the pipe is <a href="#BROKEN"> {@code broken}</a>,
     *          {@link #connect(java.io.PipedOutputStream) unconnected},
     *          closed, or if an I/O error occurs.
     * @since   1.1
     */
    protected synchronized void receive(int b) throws IOException {
        checkStateForReceive();
        writeSide = Thread.currentThread();
        if (in == out)
            awaitSpace();
        if (in < 0) {
            in = 0;
            out = 0;
        }
        buffer[in++] = (byte)(b & 0xFF);
        if (in >= buffer.length) {
            in = 0;
        }
    }

    /**
     * Receives data into an array of bytes.  This method will
     * block until some input is available.
     * @param    b the buffer into which the data is received
     * @param    off the start offset of the data
     * @param    len the maximum number of bytes received
     * @throws   IOException If the pipe is <a href="#BROKEN"> broken</a>,
     *           {@link #connect(java.io.PipedOutputStream) unconnected},
     *           closed, or if an I/O error occurs.
     */
    synchronized void receive(byte[] b, int off, int len)  throws IOException {
        checkStateForReceive();
        writeSide = Thread.currentThread();
        int bytesToTransfer = len;
        while (bytesToTransfer > 0) {
            if (in == out)
                awaitSpace();
            int nextTransferAmount = 0;
            if (out < in) {
                nextTransferAmount = buffer.length - in;
            } else if (in < out) {
                if (in == -1) {
                    in = out = 0;
                    nextTransferAmount = buffer.length - in;
                } else {
                    nextTransferAmount = out - in;
                }
            }
            if (nextTransferAmount > bytesToTransfer)
                nextTransferAmount = bytesToTransfer;
            assert(nextTransferAmount > 0);
            System.arraycopy(b, off, buffer, in, nextTransferAmount);
            bytesToTransfer -= nextTransferAmount;
            off += nextTransferAmount;
            in += nextTransferAmount;
            if (in >= buffer.length) {
                in = 0;
            }
        }
    }

    private void checkStateForReceive() 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");
        }
    }

    private void awaitSpace() throws IOException {
        while (in == out) {
            checkStateForReceive();

            /* full: kick any waiting readers */
            notifyAll();
            try {
                wait(1000);
            } catch (InterruptedException ex) {
                throw new java.io.InterruptedIOException();
            }
        }
    }

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

    /**
     * Reads the next byte of data from this piped input stream. The
     * value byte is returned as an {@code int} in the range
     * {@code 0} to {@code 255}.
     * This method blocks until input data is available, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return   {@inheritDoc}
     * @throws   IOException  if the pipe is
     *           {@link #connect(java.io.PipedOutputStream) unconnected},
     *           <a href="#BROKEN"> {@code broken}</a>, closed,
     *           or if an I/O error occurs.
     */
    @Override
    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++] & 0xFF;
        if (out >= buffer.length) {
            out = 0;
        }
        if (in == out) {
            /* now empty */
            in = -1;
        }

        return ret;
    }

    /**
     * Reads up to {@code len} bytes of data from this piped input
     * stream into an array of bytes. Less than {@code len} bytes
     * will be read if the end of the data stream is reached or if
     * {@code len} exceeds the pipe's buffer size.
     * If {@code len } is zero, then no bytes are read and 0 is returned;
     * otherwise, the method blocks until at least 1 byte of input is
     * available, end of the stream has been detected, or an exception is
     * thrown.
     *
     * @param      b     {@inheritDoc}
     * @param      off   {@inheritDoc}
     * @param      len   {@inheritDoc}
     * @return     {@inheritDoc}
     * @throws     NullPointerException {@inheritDoc}
     * @throws     IndexOutOfBoundsException {@inheritDoc}
     * @throws     IOException if the pipe is <a href="#BROKEN"> {@code broken}</a>,
     *           {@link #connect(java.io.PipedOutputStream) unconnected},
     *           closed, or if an I/O error occurs.
     */
    @Override
    public synchronized int read(byte[] b, int off, int len)  throws IOException {
        if (b == null) {
            throw new NullPointerException();
        }
        Objects.checkFromIndexSize(off, len, b.length);
        if (len == 0) {
            return 0;
        }

        /* possibly wait on the first character */
        int c = read();
        if (c < 0) {
            return -1;
        }
        b[off] = (byte) c;
        int rlen = 1;
        while ((in >= 0) && (len > 1)) {

            int available;

            if (in > out) {
                available = Math.min((buffer.length - out), (in - out));
            } else {
                available = buffer.length - out;
            }

            // A byte is read beforehand outside the loop
            if (available > (len - 1)) {
                available = len - 1;
            }
            System.arraycopy(buffer, out, b, off + rlen, available);
            out += available;
            rlen += available;
            len -= available;

            if (out >= buffer.length) {
                out = 0;
            }
            if (in == out) {
                /* now empty */
                in = -1;
            }
        }
        return rlen;
    }

    /**
     * Returns the number of bytes that can be read from this input
     * stream without blocking.
     *
     * @return the number of bytes that can be read from this input stream
     *         without blocking, or {@code 0} if this input stream has been
     *         closed by invoking its {@link #close()} method, or if the pipe
     *         is {@link #connect(java.io.PipedOutputStream) unconnected}, or
     *         <a href="#BROKEN"> {@code broken}</a>.
     *
     * @throws IOException  {@inheritDoc}
     * @since  1.0.2
     */
    @Override
    public synchronized int available() throws IOException {
        if(in < 0)
            return 0;
        else if(in == out)
            return buffer.length;
        else if (in > out)
            return in - out;
        else
            return in + buffer.length - out;
    }

    /**
     * {@inheritDoc}
     *
     * @throws     IOException  {@inheritDoc}
     */
    @Override
    public void close()  throws IOException {
        closedByReader = true;
        synchronized (this) {
            in = -1;
        }
    }
}