/*
* @(#)PipedInputStream.java 1.35 03/12/19
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
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 PipedInputStream
* object by one thread and data is written
* to the corresponding 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.
*
* @author James Gosling
* @version 1.35, 12/19/03
* @see java.io.PipedOutputStream
* @since JDK1.0
*/
public
class PipedInputStream extends InputStream {
boolean closedByWriter = false;
volatile 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.
* @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];
/**
* 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. in<0
implies the buffer is empty,
* in==out
implies the buffer is full
* @since JDK1.1
*/
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 JDK1.1
*/
protected int out = 0;
/**
* Creates a PipedInputStream
so
* that it is connected to the piped output
* stream src
. Data bytes written
* to src
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 {
connect(src);
}
/**
* Creates a PipedInputStream
so
* that it is not yet connected. It must be
* connected to a PipedOutputStream
* before being used.
*
* @see java.io.PipedInputStream#connect(java.io.PipedOutputStream)
* @see java.io.PipedOutputStream#connect(java.io.PipedInputStream)
*/
public PipedInputStream() {
}
/**
* Causes this piped input stream to be connected
* to the piped output stream src
.
* If this object is already connected to some
* other piped output stream, an IOException
* is thrown.
*
* If src
is an
* unconnected piped output stream and snk
* is an unconnected piped input stream, they
* may be connected by either the call:
*
*
snk.connect(src)
* * or the call: *
*
src.connect(snk)
*
* 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 broken.
* @since JDK1.1
*/
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 an I/O error has occurred.
*/
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) {
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();
}
}
}
/**
* 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 int
in the range
* 0
to 255
. If no byte is available
* because the end of the stream has been reached, the value
* -1
is returned. This method blocks until input data
* is available, the end of the stream is detected, or an exception
* is thrown.
* If a thread was providing data bytes
* to the connected piped output stream, but
* the thread is no longer alive, then an
* IOException
is thrown.
*
* @return the next byte of data, or -1
if the end of the
* stream is reached.
* @exception IOException if the pipe is broken.
*/
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 len
bytes of data from this piped input
* stream into an array of bytes. Less than len
bytes
* will be read if the end of the data stream is reached. This method
* blocks until at least one byte of input is available.
* If a thread was providing data bytes
* to the connected piped output stream, but
* the thread is no longer alive, then an
* IOException
is thrown.
*
* @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
* -1
if there is no more data because the end of
* the stream has been reached.
* @exception IOException 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) || (off > b.length) || (len < 0) ||
((off + len) > b.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;
}
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 available
* 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.
*/
public void close() throws IOException {
closedByReader = true;
synchronized (this) {
in = -1;
}
}
}