/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.io;
import java.util.Arrays;
import libcore.io.IoUtils;
/**
* Receives information on a communications pipe. When two threads want to pass
* data back and forth, one creates a piped writer and the other creates a piped
* reader.
*
* @see PipedWriter
*/
public class PipedReader extends Reader {
private Thread lastReader;
private Thread lastWriter;
boolean isClosed;
/**
* The circular buffer through which data is passed. Data is read from the
* range {@code [out, in)} and written to the range {@code [in, out)}.
* Data in the buffer is either sequential: <pre>
* { - - - X X X X X X X - - - - - }
* ^ ^
* | |
* out in</pre>
* ...or wrapped around the buffer's end: <pre>
* { X X X X - - - - - - - - X X X }
* ^ ^
* | |
* in out</pre>
* When the buffer is empty, {@code in == -1}. Reading when the buffer is
* empty will block until data is available. When the buffer is full,
* {@code in == out}. Writing when the buffer is full will block until free
* space is available.
*/
private char[] buffer;
/**
* The index in {@code buffer} where the next character will be written.
*/
private int in = -1;
/**
* The index in {@code buffer} where the next character will be read.
*/
private int out;
/**
* The size of the default pipe in characters
*/
private static final int PIPE_SIZE = 1024;
/**
* Indicates if this pipe is connected
*/
boolean isConnected;
/**
* Constructs a new unconnected {@code PipedReader}. The resulting reader
* must be connected to a {@code PipedWriter} before data may be read from
* it.
*/
public PipedReader() {}
/**
* Constructs a new {@code PipedReader} connected to the {@link PipedWriter}
* {@code out}. Any data written to the writer can be read from the this
* reader.
*
* @param out
* the {@code PipedWriter} to connect to.
* @throws IOException
* if {@code out} is already connected.
*/
public PipedReader(PipedWriter out) throws IOException {
connect(out);
}
/**
* Constructs a new unconnected {@code PipedReader} with the given buffer size.
* The resulting reader must be connected to a {@code PipedWriter} before
* data may be read from it.
*
* @param pipeSize the size of the buffer in chars.
* @throws IllegalArgumentException if pipeSize is less than or equal to zero.
* @since 1.6
*/
public PipedReader(int pipeSize) {
if (pipeSize <= 0) {
throw new IllegalArgumentException("pipe size " + pipeSize + " too small");
}
buffer = new char[pipeSize];
}
/**
* Constructs a new {@code PipedReader} connected to the given {@code PipedWriter},
* with the given buffer size. Any data written to the writer can be read from
* this reader.
*
* @param out the {@code PipedWriter} to connect to.
* @param pipeSize the size of the buffer in chars.
* @throws IOException if an I/O error occurs
* @throws IllegalArgumentException if pipeSize is less than or equal to zero.
* @since 1.6
*/
public PipedReader(PipedWriter out, int pipeSize) throws IOException {
this(pipeSize);
connect(out);
}
/**
* Closes this reader. This implementation releases the buffer used for
* the pipe and notifies all threads waiting to read or write.
*
* @throws IOException
* if an error occurs while closing this reader.
*/
@Override
public synchronized void close() throws IOException {
buffer = null;
isClosed = true;
notifyAll();
}
/**
* Connects this {@code PipedReader} to a {@link PipedWriter}. Any data
* written to the writer becomes readable in this reader.
*
* @param src
* the writer to connect to.
* @throws IOException
* if this reader is closed or already connected, or if {@code
* src} is already connected.
*/
public void connect(PipedWriter src) throws IOException {
src.connect(this);
}
/**
* Establishes the connection to the PipedWriter.
*
* @throws IOException
* If this Reader is already connected.
*/
synchronized void establishConnection() throws IOException {
if (isConnected) {
throw new IOException("Pipe already connected");
}
if (isClosed) {
throw new IOException("Pipe is closed");
}
if (buffer == null) { // We may already have allocated the buffer.
buffer = new char[PIPE_SIZE];
}
isConnected = true;
}
/**
* Reads a single character from this reader and returns it as an integer
* with the two higher-order bytes set to 0. Returns -1 if the end of the
* reader has been reached. If there is no data in the pipe, this method
* blocks until data is available, the end of the reader is detected or an
* exception is thrown.
* <p>
* Separate threads should be used to read from a {@code PipedReader} and to
* write to the connected {@link PipedWriter}. If the same thread is used,
* a deadlock may occur.
*
* @return the character read or -1 if the end of the reader has been
* reached.
* @throws IOException
* if this reader is closed or some other I/O error occurs.
*/
@Override
public int read() throws IOException {
char[] chars = new char[1];
int result = read(chars, 0, 1);
return result != -1 ? chars[0] : result;
}
/**
* Reads up to {@code count} characters from this reader and stores them
* in the character array {@code buffer} starting at {@code offset}. If
* there is no data in the pipe, this method blocks until at least one byte
* has been read, the end of the reader is detected or an exception is
* thrown.
*
* <p>Separate threads should be used to read from a {@code PipedReader} and to
* write to the connected {@link PipedWriter}. If the same thread is used, a
* deadlock may occur.
*
* <p>Returns the number of characters read or -1 if the end of the reader has
* been reached.
*
* @throws IndexOutOfBoundsException
* if {@code offset < 0 || count < 0 || offset + count > buffer.length}.
* @throws InterruptedIOException
* if the thread reading from this reader is interrupted.
* @throws IOException
* if this reader is closed or not connected to a writer, or if
* the thread writing to the connected writer is no longer
* alive.
*/
@Override public synchronized int read(char[] buffer, int offset, int count) throws IOException {
if (!isConnected) {
throw new IOException("Pipe not connected");
}
if (this.buffer == null) {
throw new IOException("Pipe is closed");
}
Arrays.checkOffsetAndCount(buffer.length, offset, count);
if (count == 0) {
return 0;
}
/**
* Set the last thread to be reading on this PipedReader. If
* lastReader dies while someone is waiting to write an IOException
* of "Pipe broken" will be thrown in receive()
*/
lastReader = Thread.currentThread();
try {
boolean first = true;
while (in == -1) {
// Are we at end of stream?
if (isClosed) {
return -1;
}
if (!first && lastWriter != null && !lastWriter.isAlive()) {
throw new IOException("Pipe broken");
}
first = false;
// Notify callers of receive()
notifyAll();
wait(1000);
}
} catch (InterruptedException e) {
IoUtils.throwInterruptedIoException();
}
int copyLength = 0;
/* Copy chars from out to end of buffer first */
if (out >= in) {
copyLength = count > this.buffer.length - out ? this.buffer.length - out : count;
System.arraycopy(this.buffer, out, buffer, offset, copyLength);
out += copyLength;
if (out == this.buffer.length) {
out = 0;
}
if (out == in) {
// empty buffer
in = -1;
out = 0;
}
}
/*
* Did the read fully succeed in the previous copy or is the buffer
* empty?
*/
if (copyLength == count || in == -1) {
return copyLength;
}
int charsCopied = copyLength;
/* Copy bytes from 0 to the number of available bytes */
copyLength = in - out > count - copyLength ? count - copyLength : in - out;
System.arraycopy(this.buffer, out, buffer, offset + charsCopied, copyLength);
out += copyLength;
if (out == in) {
// empty buffer
in = -1;
out = 0;
}
return charsCopied + copyLength;
}
/**
* Indicates whether this reader is ready to be read without blocking.
* Returns {@code true} if this reader will not block when {@code read} is
* called, {@code false} if unknown or blocking will occur. This
* implementation returns {@code true} if the internal buffer contains
* characters that can be read.
*
* @return always {@code false}.
* @throws IOException
* if this reader is closed or not connected, or if some other
* I/O error occurs.
* @see #read()
* @see #read(char[], int, int)
*/
@Override
public synchronized boolean ready() throws IOException {
if (!isConnected) {
throw new IOException("Pipe not connected");
}
if (buffer == null) {
throw new IOException("Pipe is closed");
}
return in != -1;
}
/**
* Receives a char and stores it into the PipedReader. This called by
* PipedWriter.write() when writes occur.
* <P>
* If the buffer is full and the thread sending #receive is interrupted, the
* InterruptedIOException will be thrown.
*
* @param oneChar
* the char to store into the pipe.
*
* @throws IOException
* If the stream is already closed or another IOException
* occurs.
*/
synchronized void receive(char oneChar) throws IOException {
if (buffer == null) {
throw new IOException("Pipe is closed");
}
if (lastReader != null && !lastReader.isAlive()) {
throw new IOException("Pipe broken");
}
/*
* Set the last thread to be writing on this PipedWriter. If
* lastWriter dies while someone is waiting to read an IOException
* of "Pipe broken" will be thrown in read()
*/
lastWriter = Thread.currentThread();
try {
while (buffer != null && out == in) {
notifyAll();
wait(1000);
if (lastReader != null && !lastReader.isAlive()) {
throw new IOException("Pipe broken");
}
}
} catch (InterruptedException e) {
IoUtils.throwInterruptedIoException();
}
if (buffer == null) {
throw new IOException("Pipe is closed");
}
if (in == -1) {
in = 0;
}
buffer[in++] = oneChar;
if (in == buffer.length) {
in = 0;
}
}
/**
* Receives a char array and stores it into the PipedReader. This called by
* PipedWriter.write() when writes occur.
* <P>
* If the buffer is full and the thread sending #receive is interrupted, the
* InterruptedIOException will be thrown.
*
* @throws IOException
* If the stream is already closed or another IOException
* occurs.
*/
synchronized void receive(char[] chars, int offset, int count) throws IOException {
Arrays.checkOffsetAndCount(chars.length, offset, count);
if (buffer == null) {
throw new IOException("Pipe is closed");
}
if (lastReader != null && !lastReader.isAlive()) {
throw new IOException("Pipe broken");
}
/**
* Set the last thread to be writing on this PipedWriter. If
* lastWriter dies while someone is waiting to read an IOException
* of "Pipe broken" will be thrown in read()
*/
lastWriter = Thread.currentThread();
while (count > 0) {
try {
while (buffer != null && out == in) {
notifyAll();
wait(1000);
if (lastReader != null && !lastReader.isAlive()) {
throw new IOException("Pipe broken");
}
}
} catch (InterruptedException e) {
IoUtils.throwInterruptedIoException();
}
if (buffer == null) {
throw new IOException("Pipe is closed");
}
if (in == -1) {
in = 0;
}
if (in >= out) {
int length = buffer.length - in;
if (count < length) {
length = count;
}
System.arraycopy(chars, offset, buffer, in, length);
offset += length;
count -= length;
in += length;
if (in == buffer.length) {
in = 0;
}
}
if (count > 0 && in != out) {
int length = out - in;
if (count < length) {
length = count;
}
System.arraycopy(chars, offset, buffer, in, length);
offset += length;
count -= length;
in += length;
}
}
}
synchronized void done() {
isClosed = true;
notifyAll();
}
}