Circular Char Buffer
/*
* Circular Character Buffer
* Copyright (C) 2002 Stephen Ostermiller
* http://ostermiller.org/contact.pl?regarding=Java+Utilities
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 for more details.
*
* See COPYING.TXT for details.
*/
import java.io.*;
/**
* Implements the Circular Buffer producer/consumer model for characters.
* More information about this class is available from <a target="_top" href=
* "http://ostermiller.org/utils/CircularCharBuffer.html">ostermiller.org</a>.
* <p>
* Using this class is a simpler alternative to using a PipedReader
* and a PipedWriter. PipedReaders and PipedWriters don't support the
* mark operation, don't allow you to control buffer sizes that they use,
* and have a more complicated API that requires instantiating two
* classes and connecting them.
* <p>
* This class is thread safe.
*
* @see CircularByteBuffer
* @see CircularObjectBuffer
*
* @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
* @since ostermillerutils 1.00.00
*/
public class CircularCharBuffer {
/**
* The default size for a circular character buffer.
*
* @since ostermillerutils 1.00.00
*/
private final static int DEFAULT_SIZE = 1024;
/**
* A buffer that will grow as things are added.
*
* @since ostermillerutils 1.00.00
*/
public final static int INFINITE_SIZE = -1;
/**
* The circular buffer.
* <p>
* The actual capacity of the buffer is one less than the actual length
* of the buffer so that an empty and a full buffer can be
* distinguished. An empty buffer will have the markPostion and the
* writePosition equal to each other. A full buffer will have
* the writePosition one less than the markPostion.
* <p>
* There are three important indexes into the buffer:
* The readPosition, the writePosition, and the markPosition.
* If the Reader has never been marked, the readPosition and
* the markPosition should always be the same. The characters
* available to be read go from the readPosition to the writePosition,
* wrapping around the end of the buffer. The space available for writing
* goes from the write position to one less than the markPosition,
* wrapping around the end of the buffer. The characters that have
* been saved to support a reset() of the Reader go from markPosition
* to readPosition, wrapping around the end of the buffer.
*
* @since ostermillerutils 1.00.00
*/
protected char[] buffer;
/**
* Index of the first character available to be read.
*
* @since ostermillerutils 1.00.00
*/
protected volatile int readPosition = 0;
/**
* Index of the first character available to be written.
*
* @since ostermillerutils 1.00.00
*/
protected volatile int writePosition = 0;
/**
* Index of the first saved character. (To support stream marking.)
*
* @since ostermillerutils 1.00.00
*/
protected volatile int markPosition = 0;
/**
* Number of characters that have to be saved
* to support mark() and reset() on the Reader.
*
* @since ostermillerutils 1.00.00
*/
protected volatile int markSize = 0;
/**
* If this buffer is infinite (should resize itself when full)
*
* @since ostermillerutils 1.00.00
*/
protected volatile boolean infinite = false;
/**
* True if a write to a full buffer should block until the buffer
* has room, false if the write method should throw an IOException
*
* @since ostermillerutils 1.00.00
*/
protected boolean blockingWrite = true;
/**
* The Reader that can empty this buffer.
*
* @since ostermillerutils 1.00.00
*/
protected Reader reader = new CircularCharBufferReader();
/**
* true if the close() method has been called on the Reader
*
* @since ostermillerutils 1.00.00
*/
protected boolean readerClosed = false;
/**
* The Writer that can fill this buffer.
*
* @since ostermillerutils 1.00.00
*/
protected Writer writer = new CircularCharBufferWriter();
/**
* true if the close() method has been called on the writer
*
* @since ostermillerutils 1.00.00
*/
protected boolean writerClosed = false;
/**
* Make this buffer ready for reuse. The contents of the buffer
* will be cleared and the streams associated with this buffer
* will be reopened if they had been closed.
*
* @since ostermillerutils 1.00.00
*/
public void clear(){
synchronized (this){
readPosition = 0;
writePosition = 0;
markPosition = 0;
readerClosed = false;
writerClosed = false;
}
}
/**
* Retrieve a Writer that can be used to fill
* this buffer.
* <p>
* Write methods may throw a BufferOverflowException if
* the buffer is not large enough. A large enough buffer
* size must be chosen so that this does not happen or
* the caller must be prepared to catch the exception and
* try again once part of the buffer has been consumed.
*
*
* @return the producer for this buffer.
*
* @since ostermillerutils 1.00.00
*/
public Writer getWriter(){
return writer;
}
/**
* Retrieve a Reader that can be used to empty
* this buffer.
* <p>
* This Reader supports marks at the expense
* of the buffer size.
*
* @return the consumer for this buffer.
*
* @since ostermillerutils 1.00.00
*/
public Reader getReader(){
return reader;
}
/**
* Get number of characters that are available to be read.
* <p>
* Note that the number of characters available plus
* the number of characters free may not add up to the
* capacity of this buffer, as the buffer may reserve some
* space for other purposes.
*
* @return the size in characters of this buffer
*
* @since ostermillerutils 1.00.00
*/
public int getAvailable(){
synchronized (this){
return available();
}
}
/**
* Get the number of characters this buffer has free for
* writing.
* <p>
* Note that the number of characters available plus
* the number of characters free may not add up to the
* capacity of this buffer, as the buffer may reserve some
* space for other purposes.
*
* @return the available space in characters of this buffer
*
* @since ostermillerutils 1.00.00
*/
public int getSpaceLeft(){
synchronized (this){
return spaceLeft();
}
}
/**
* Get the capacity of this buffer.
* <p>
* Note that the number of characters available plus
* the number of characters free may not add up to the
* capacity of this buffer, as the buffer may reserve some
* space for other purposes.
*
* @return the size in characters of this buffer
*
* @since ostermillerutils 1.00.00
*/
public int getSize(){
synchronized (this){
return buffer.length;
}
}
/**
* double the size of the buffer
*
* @since ostermillerutils 1.00.00
*/
private void resize(){
char[] newBuffer = new char[buffer.length * 2];
int marked = marked();
int available = available();
if (markPosition <= writePosition){
// any space between the mark and
// the first write needs to be saved.
// In this case it is all in one piece.
int length = writePosition - markPosition;
System.arraycopy(buffer, markPosition, newBuffer, 0, length);
} else {
int length1 = buffer.length - markPosition;
System.arraycopy(buffer, markPosition, newBuffer, 0, length1);
int length2 = writePosition;
System.arraycopy(buffer, 0, newBuffer, length1, length2);
}
buffer = newBuffer;
markPosition = 0;
readPosition = marked;
writePosition = marked + available;
}
/**
* Space available in the buffer which can be written.
*
* @since ostermillerutils 1.00.00
*/
private int spaceLeft(){
if (writePosition < markPosition){
// any space between the first write and
// the mark except one character is available.
// In this case it is all in one piece.
return (markPosition - writePosition - 1);
}
// space at the beginning and end.
return ((buffer.length - 1) - (writePosition - markPosition));
}
/**
* Characters available for reading.
*
* @since ostermillerutils 1.00.00
*/
private int available(){
if (readPosition <= writePosition){
// any space between the first read and
// the first write is available. In this case i
// is all in one piece.
return (writePosition - readPosition);
}
// space at the beginning and end.
return (buffer.length - (readPosition - writePosition));
}
/**
* Characters saved for supporting marks.
*
* @since ostermillerutils 1.00.00
*/
private int marked(){
if (markPosition <= readPosition){
// any space between the markPosition and
// the first write is marked. In this case i
// is all in one piece.
return (readPosition - markPosition);
}
// space at the beginning and end.
return (buffer.length - (markPosition - readPosition));
}
/**
* If we have passed the markSize reset the
* mark so that the space can be used.
*
* @since ostermillerutils 1.00.00
*/
private void ensureMark(){
if (marked() >= markSize){
markPosition = readPosition;
markSize = 0;
}
}
/**
* Create a new buffer with a default capacity.
* Writing to a full buffer will block until space
* is available rather than throw an exception.
*
* @since ostermillerutils 1.00.00
*/
public CircularCharBuffer(){
this (DEFAULT_SIZE, true);
}
/**
* Create a new buffer with given capacity.
* Writing to a full buffer will block until space
* is available rather than throw an exception.
* <p>
* Note that the buffer may reserve some characters for
* special purposes and capacity number of characters may
* not be able to be written to the buffer.
* <p>
* Note that if the buffer is of INFINITE_SIZE it will
* neither block or throw exceptions, but rather grow
* without bound.
*
* @param size desired capacity of the buffer in characters or CircularCharBuffer.INFINITE_SIZE
*
* @since ostermillerutils 1.00.00
*/
public CircularCharBuffer(int size){
this (size, true);
}
/**
* Create a new buffer with a default capacity and
* given blocking behavior.
*
* @param blockingWrite true writing to a full buffer should block
* until space is available, false if an exception should
* be thrown instead.
*
* @since ostermillerutils 1.00.00
*/
public CircularCharBuffer(boolean blockingWrite){
this (DEFAULT_SIZE, blockingWrite);
}
/**
* Create a new buffer with the given capacity and
* blocking behavior.
* <p>
* Note that the buffer may reserve some characters for
* special purposes and capacity number of characters may
* not be able to be written to the buffer.
* <p>
* Note that if the buffer is of CircularCharBuffer.INFINITE_SIZE it will
* neither block or throw exceptions, but rather grow
* without bound.
*
* @param size desired capacity of the buffer in characters or CircularCharBuffer.INFINITE_SIZE
* @param blockingWrite true writing to a full buffer should block
* until space is available, false if an exception should
* be thrown instead.
*
* @since ostermillerutils 1.00.00
*/
public CircularCharBuffer(int size, boolean blockingWrite){
if (size == INFINITE_SIZE){
buffer = new char[DEFAULT_SIZE];
infinite = true;
} else {
buffer = new char[size];
infinite = false;
}
this.blockingWrite = blockingWrite;
}
/**
* Class for reading from a circular character buffer.
*
* @since ostermillerutils 1.00.00
*/
protected class CircularCharBufferReader extends Reader {
/**
* Close the stream. Once a stream has been closed, further read(), ready(),
* mark(), or reset() invocations will throw an IOException. Closing a
* previously-closed stream, however, has no effect.
*
* @throws IOException never.
*
* @since ostermillerutils 1.00.00
*/
@Override public void close() throws IOException {
synchronized (CircularCharBuffer.this){
readerClosed = true;
}
}
/**
* Mark the present position in the stream. Subsequent calls to reset() will
* attempt to reposition the stream to this point.
* <p>
* The readAheadLimit must be less than the size of circular buffer.
*
* @param readAheadLimit Limit on the number of characters that may be read while
* still preserving the mark. After reading this many characters, attempting to
* reset the stream will fail.
* @throws IOException if the stream is closed, or the buffer size is greater
* than or equal to the readAheadLimit.
*
* @since ostermillerutils 1.00.00
*/
@Override public void mark(int readAheadLimit) throws IOException {
synchronized (CircularCharBuffer.this){
if (readerClosed) throw new IOException("Reader has been closed; cannot mark a closed Reader.");
if (buffer.length - 1 <= readAheadLimit) throw new IOException("Cannot mark stream, readAheadLimit bigger than buffer size.");
markSize = readAheadLimit;
markPosition = readPosition;
}
}
/**
* Tell whether this stream supports the mark() operation.
*
* @return true, mark is supported.
*
* @since ostermillerutils 1.00.00
*/
@Override public boolean markSupported() {
return true;
}
/**
* Read a single character.
* This method will block until a character is available, an I/O error occurs,
* or the end of the stream is reached.
*
* @return The character read, as an integer in the range 0 to 65535 (0x00-0xffff),
* or -1 if the end of the stream has been reached
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int read() throws IOException {
while (true){
synchronized (CircularCharBuffer.this){
if (readerClosed) throw new IOException("Reader has been closed; cannot read from a closed Reader.");
int available = available();
if (available > 0){
int result = buffer[readPosition] & 0xffff;
readPosition++;
if (readPosition == buffer.length){
readPosition = 0;
}
ensureMark();
return result;
} else if (writerClosed){
return -1;
}
}
try {
Thread.sleep(100);
} catch(Exception x){
throw new IOException("Blocking read operation interrupted.");
}
}
}
/**
* Read characters into an array.
* This method will block until some input is available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer.
* @return The number of characters read, or -1 if the end of
* the stream has been reached
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int read(char[] cbuf) throws IOException {
return read(cbuf, 0, cbuf.length);
}
/**
* Read characters into a portion of an array.
* This method will block until some input is available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer.
* @param off Offset at which to start storing characters.
* @param len Maximum number of characters to read.
* @return The number of characters read, or -1 if the end of
* the stream has been reached
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public int read(char[] cbuf, int off, int len) throws IOException {
while (true){
synchronized (CircularCharBuffer.this){
if (readerClosed) throw new IOException("Reader has been closed; cannot read from a closed Reader.");
int available = available();
if (available > 0){
int length = Math.min(len, available);
int firstLen = Math.min(length, buffer.length - readPosition);
int secondLen = length - firstLen;
System.arraycopy(buffer, readPosition, cbuf, off, firstLen);
if (secondLen > 0){
System.arraycopy(buffer, 0, cbuf, off+firstLen, secondLen);
readPosition = secondLen;
} else {
readPosition += length;
}
if (readPosition == buffer.length) {
readPosition = 0;
}
ensureMark();
return length;
} else if (writerClosed){
return -1;
}
}
try {
Thread.sleep(100);
} catch(Exception x){
throw new IOException("Blocking read operation interrupted.");
}
}
}
/**
* Tell whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input,
* false otherwise. Note that returning false does not guarantee that
* the next read will block.
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public boolean ready() throws IOException {
synchronized (CircularCharBuffer.this){
if (readerClosed) throw new IOException("Reader has been closed, it is not ready.");
return (available() > 0);
}
}
/**
* Reset the stream.
* If the stream has been marked, then attempt to reposition i
* at the mark. If the stream has not been marked, or more characters
* than the readAheadLimit have been read, this method has no effect.
*
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public void reset() throws IOException {
synchronized (CircularCharBuffer.this){
if (readerClosed) throw new IOException("Reader has been closed; cannot reset a closed Reader.");
readPosition = markPosition;
}
}
/**
* Skip characters.
* This method will block until some characters are available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param n The number of characters to skip
* @return The number of characters actually skipped
* @throws IllegalArgumentException if n is negative.
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public long skip(long n) throws IOException, IllegalArgumentException {
while (true){
synchronized (CircularCharBuffer.this){
if (readerClosed) throw new IOException("Reader has been closed; cannot skip characters on a closed Reader.");
int available = available();
if (available > 0){
int length = Math.min((int)n, available);
int firstLen = Math.min(length, buffer.length - readPosition);
int secondLen = length - firstLen;
if (secondLen > 0){
readPosition = secondLen;
} else {
readPosition += length;
}
if (readPosition == buffer.length) {
readPosition = 0;
}
ensureMark();
return length;
} else if (writerClosed){
return 0;
}
}
try {
Thread.sleep(100);
} catch(Exception x){
throw new IOException("Blocking read operation interrupted.");
}
}
}
}
/**
* Class for writing to a circular character buffer.
* If the buffer is full, the writes will either block
* until there is some space available or throw an IOException
* based on the CircularCharBuffer's preference.
*
* @since ostermillerutils 1.00.00
*/
protected class CircularCharBufferWriter extends Writer {
/**
* Close the stream, flushing it first.
* This will cause the reader associated with this circular buffer
* to read its last characters once it empties the buffer.
* Once a stream has been closed, further write() or flush() invocations
* will cause an IOException to be thrown. Closing a previously-closed stream,
* however, has no effect.
*
* @throws IOException never.
*
* @since ostermillerutils 1.00.00
*/
@Override public void close() throws IOException {
synchronized (CircularCharBuffer.this){
if (!writerClosed){
flush();
}
writerClosed = true;
}
}
/**
* Flush the stream.
*
* @throws IOException if the stream is closed.
*
* @since ostermillerutils 1.00.00
*/
@Override public void flush() throws IOException {
if (writerClosed) throw new IOException("Writer has been closed; cannot flush a closed Writer.");
if (readerClosed) throw new IOException("Buffer closed by Reader; cannot flush.");
// this method needs to do nothing
}
/**
* Write an array of characters.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param cbuf Array of characters to be written
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full. If the exception is thrown, no data
* will have been written since the buffer was set to be non-blocking.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(char[] cbuf) throws IOException {
write(cbuf, 0, cbuf.length);
}
/**
* Write a portion of an array of characters.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param cbuf Array of characters
* @param off Offset from which to start writing characters
* @param len - Number of characters to write
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full. If the exception is thrown, no data
* will have been written since the buffer was set to be non-blocking.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(char[] cbuf, int off, int len) throws IOException {
while (len > 0){
synchronized (CircularCharBuffer.this){
if (writerClosed) throw new IOException("Writer has been closed; cannot write to a closed Writer.");
if (readerClosed) throw new IOException("Buffer closed by Reader; cannot write to a closed buffer.");
int spaceLeft = spaceLeft();
while (infinite && spaceLeft < len){
resize();
spaceLeft = spaceLeft();
}
if (!blockingWrite && spaceLeft < len) throw new Exception("CircularCharBuffer is full; cannot write " + len + " characters");
int realLen = Math.min(len, spaceLeft);
int firstLen = Math.min(realLen, buffer.length - writePosition);
int secondLen = Math.min(realLen - firstLen, buffer.length - markPosition - 1);
int written = firstLen + secondLen;
if (firstLen > 0){
System.arraycopy(cbuf, off, buffer, writePosition, firstLen);
}
if (secondLen > 0){
System.arraycopy(cbuf, off+firstLen, buffer, 0, secondLen);
writePosition = secondLen;
} else {
writePosition += written;
}
if (writePosition == buffer.length) {
writePosition = 0;
}
off += written;
len -= written;
}
if (len > 0){
try {
Thread.sleep(100);
} catch(Exception x){
throw new IOException("Waiting for available space in buffer interrupted.");
}
}
}
}
/**
* Write a single character.
* The character to be written is contained in the 16 low-order bits of the
* given integer value; the 16 high-order bits are ignored.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param c number of characters to be written
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(int c) throws IOException {
boolean written = false;
while (!written){
synchronized (CircularCharBuffer.this){
if (writerClosed) throw new IOException("Writer has been closed; cannot write to a closed Writer.");
if (readerClosed) throw new IOException("Buffer closed by Reader; cannot write to a closed buffer.");
int spaceLeft = spaceLeft();
while (infinite && spaceLeft < 1){
resize();
spaceLeft = spaceLeft();
}
if (!blockingWrite && spaceLeft < 1) throw new Exception("CircularCharBuffer is full; cannot write 1 character");
if (spaceLeft > 0){
buffer[writePosition] = (char)(c & 0xffff);
writePosition++;
if (writePosition == buffer.length) {
writePosition = 0;
}
written = true;
}
}
if (!written){
try {
Thread.sleep(100);
} catch(Exception x){
throw new IOException("Waiting for available space in buffer interrupted.");
}
}
}
}
/**
* Write a string.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param str String to be written
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full. If the exception is thrown, no data
* will have been written since the buffer was set to be non-blocking.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(String str) throws IOException {
write(str, 0, str.length());
}
/**
* Write a portion of a string.
* If the buffer allows blocking writes, this method will block until
* all the data has been written rather than throw an IOException.
*
* @param str A String
* @param off Offset from which to start writing characters
* @param len Number of characters to write
* @throws BufferOverflowException if buffer does not allow blocking writes
* and the buffer is full. If the exception is thrown, no data
* will have been written since the buffer was set to be non-blocking.
* @throws IOException if the stream is closed, or the write is interrupted.
*
* @since ostermillerutils 1.00.00
*/
@Override public void write(String str, int off, int len) throws IOException {
while (len > 0){
synchronized (CircularCharBuffer.this){
if (writerClosed) throw new IOException("Writer has been closed; cannot write to a closed Writer.");
if (readerClosed) throw new IOException("Buffer closed by Reader; cannot write to a closed buffer.");
int spaceLeft = spaceLeft();
while (infinite && spaceLeft < len){
resize();
spaceLeft = spaceLeft();
}
if (!blockingWrite && spaceLeft < len) throw new Exception("CircularCharBuffer is full; cannot write " + len + " characters");
int realLen = Math.min(len, spaceLeft);
int firstLen = Math.min(realLen, buffer.length - writePosition);
int secondLen = Math.min(realLen - firstLen, buffer.length - markPosition - 1);
int written = firstLen + secondLen;
for (int i=0; i<firstLen; i++){
buffer[writePosition + i] = str.charAt(off+i);
}
if (secondLen > 0){
for (int i=0; i<secondLen; i++){
buffer[i] = str.charAt(off+firstLen+i);
}
writePosition = secondLen;
} else {
writePosition += written;
}
if (writePosition == buffer.length) {
writePosition = 0;
}
off += written;
len -= written;
}
if (len > 0){
try {
Thread.sleep(100);
} catch(Exception x){
throw new IOException("Waiting for available space in buffer interrupted.");
}
}
}
}
}
}
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