Java example source code file (PipedReader.java)
The PipedReader.java Java example source code/*
* Copyright (c) 1996, 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;
/**
* Piped character-input streams.
*
* @author Mark Reinhold
* @since JDK1.1
*/
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.
*/
private static final int DEFAULT_PIPE_SIZE = 1024;
/**
* 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. <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.
*/
int out = 0;
/**
* Creates a <code>PipedReader so
* that it is connected to the piped writer
* <code>src. Data written to
* <p>
* or the call:
*
* <pre>src.connect(snk)
* <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.
*/
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.
*/
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.
*/
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 <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.
* @exception IOException if the pipe is
* <a href=PipedInputStream.html#BROKEN> broken,
* {@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 <code>len characters of data from this piped
* stream into an array of characters. Less than <code>len characters
* will be read if the end of the data stream is reached or if
* <code>len 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 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> broken,
* {@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");
}
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.
*
* @exception IOException if the pipe is
* <a href=PipedInputStream.html#BROKEN> broken,
* {@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.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {
in = -1;
closedByReader = true;
}
}
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