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PipedInputStream.java
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1998-09-22
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/*
* @(#)PipedInputStream.java 1.19 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
package java.io;
/**
* A piped input stream is the receiving end of a communications
* pipe. Two threads can communicate by having one thread send data
* through a piped output stream and having the other thread read the
* data through a piped input stream.
*
* @author James Gosling
* @version 1.19, 07/01/98
* @see java.io.PipedOutputStream
* @since JDK1.0
*/
public
class PipedInputStream extends InputStream {
boolean closed = true;
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;
/**
* @since JDK1.1
*/
protected static final int PIPE_SIZE = 1024;
/**
* The circular buffer into which incoming data is placed.
* @since JDK1.1
*/
protected byte buffer[] = new byte[PIPE_SIZE];
/*
* fill and empty pointers. in<0 implies the buffer is empty, in==out
* implies the buffer is full
*/
/**
* @since JDK1.1
*/
protected int in = -1;
/**
* @since JDK1.1
*/
protected int out = 0;
/**
* Creates a piped input stream connected to the specified piped
* output stream.
*
* @param src the stream to connect to.
* @exception IOException if an I/O error occurs.
* @since JDK1.0
*/
public PipedInputStream(PipedOutputStream src) throws IOException {
connect(src);
}
/**
* Creates a piped input stream that is not yet connected to a piped
* output stream. It must be connected to a piped output 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)
* @since JDK1.0
*/
public PipedInputStream() {
}
/**
* Connects this piped input stream to a sender.
*
* @param src The piped output stream to connect to.
* @exception IOException if an I/O error occurs.
* @since JDK1.0
*/
public void connect(PipedOutputStream src) throws IOException {
if (connected) {
throw new IOException("Pipe already connected");
}
src.connect(this);
connected = true;
}
/**
* 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 broken.
* @since JDK1.1
*/
protected synchronized void receive(int b) throws IOException {
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++] = (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
* @return the actual number of bytes received, -1 is
* returned when the end of the stream is reached.
* @exception IOException If an I/O error has occurred.
*/
synchronized void receive(byte b[], int off, int len) throws IOException {
while (--len >= 0) {
receive(b[off++]);
}
}
/**
* Notifies all waiting threads that the last byte of data has been
* received.
*/
synchronized void receivedLast() {
closed = 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>. If no byte is available
* because this end of the stream has been reached, the value
* <code>-1</code> 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 byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @exception IOException if the pipe is broken.
* @since JDK1.0
*/
public synchronized int read() throws IOException {
if (closedByReader) {
throw new IOException("InputStream closed");
}
int trials = 2;
while (in < 0) {
readSide = Thread.currentThread();
if (closed) {
/* 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. This method blocks until at least one
* byte of input is available.
*
* @param b the buffer into which the data is read.
* @param off the start offset of the data.
* @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 IOException if an I/O error occurs.
* @since JDK1.0
*/
public synchronized int read(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || off + len > b.length) {
throw new ArrayIndexOutOfBoundsException();
} 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 > 0)) {
b[off + rlen] = buffer[out++];
rlen++;
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. This method overrides the <code>available</code>
* method of the parent class.
*
* @return the number of bytes that can be read from this input stream
* without blocking.
* @exception IOException if an I/O error occurs.
* @since JDK1.0.2
*/
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.
* @since JDK1.0
*/
public void close() throws IOException {
in = -1;
closedByReader = true;
}
}