Java tutorial
/* * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.io; /** * 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</code> * object by one thread and data is written * to the corresponding <code>PipedOutputStream</code> * 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</code> implies the buffer is empty, * <code>in==out</code> 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</code> so * that it is connected to the piped output * stream <code>src</code>. Data bytes 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 PipedInputStream(PipedOutputStream src) throws IOException { this(src, DEFAULT_PIPE_SIZE); } /** * Creates a <code>PipedInputStream</code> so that it is * connected to the piped output stream * <code>src</code> and uses the specified pipe size for * the pipe's buffer. * Data bytes 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 PipedInputStream(PipedOutputStream src, int pipeSize) throws IOException { initPipe(pipeSize); connect(src); } /** * Creates a <code>PipedInputStream</code> 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</code> before being used. */ public PipedInputStream() { initPipe(DEFAULT_PIPE_SIZE); } /** * Creates a <code>PipedInputStream</code> 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</code> before being used. * * @param pipeSize the size of the pipe's buffer. * @exception 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</code>. * If this object is already connected to some * other piped output stream, an <code>IOException</code> * is thrown. * <p> * If <code>src</code> is an * unconnected piped output stream and <code>snk</code> * is an unconnected piped input stream, 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 output stream to connect to. * @exception 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 * @exception IOException If the pipe is <a href="#BROKEN"> <code>broken</code></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 * @exception 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</code> in the range * <code>0</code> to <code>255</code>. * This method blocks until input data is available, the end of the * stream is detected, or an exception is thrown. * * @return the next byte of data, or <code>-1</code> if the end of the * stream is reached. * @exception IOException if the pipe is * {@link #connect(java.io.PipedOutputStream) unconnected}, * <a href="#BROKEN"> <code>broken</code></a>, closed, * or if 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++] & 0xFF; if (out >= buffer.length) { out = 0; } if (in == out) { /* now empty */ in = -1; } return ret; } /** * Reads up to <code>len</code> bytes of data from this piped input * stream into an array of bytes. Less than <code>len</code> bytes * will be read if the end of the data stream is reached or if * <code>len</code> exceeds the pipe's buffer size. * If <code>len </code> 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 the buffer into which the data is read. * @param off the start offset in the destination array <code>b</code> * @param len the maximum number of bytes read. * @return the total number of bytes read into the buffer, or * <code>-1</code> if there is no more data because the end of * the stream has been reached. * @exception NullPointerException If <code>b</code> is <code>null</code>. * @exception IndexOutOfBoundsException If <code>off</code> is negative, * <code>len</code> is negative, or <code>len</code> is greater than * <code>b.length - off</code> * @exception IOException if the pipe is <a href="#BROKEN"> <code>broken</code></a>, * {@link #connect(java.io.PipedOutputStream) unconnected}, * closed, or if an I/O error occurs. */ public synchronized int read(byte b[], int off, int len) throws IOException { if (b == null) { throw new NullPointerException(); } else if (off < 0 || len < 0 || len > b.length - off) { throw new IndexOutOfBoundsException(); } else 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</code></a>. * * @exception IOException if an I/O error occurs. * @since 1.0.2 */ 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; } /** * Closes this piped input stream and releases any system resources * associated with the stream. * * @exception IOException if an I/O error occurs. */ public void close() throws IOException { closedByReader = true; synchronized (this) { in = -1; } } }