package org.apache.lucene.store;
/**
* 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.
*/
import java.io.IOException;
/** Base implementation class for buffered {@link IndexInput}. */
public abstract class BufferedIndexInput extends IndexInput {
/** Default buffer size */
public static final int BUFFER_SIZE = 1024;
private int bufferSize = BUFFER_SIZE;
protected byte[] buffer;
private long bufferStart = 0; // position in file of buffer
private int bufferLength = 0; // end of valid bytes
private int bufferPosition = 0; // next byte to read
@Override
public byte readByte() throws IOException {
if (bufferPosition >= bufferLength)
refill();
return buffer[bufferPosition++];
}
public BufferedIndexInput() {}
/** Inits BufferedIndexInput with a specific bufferSize */
public BufferedIndexInput(int bufferSize) {
checkBufferSize(bufferSize);
this.bufferSize = bufferSize;
}
/** Change the buffer size used by this IndexInput */
public void setBufferSize(int newSize) {
assert buffer == null || bufferSize == buffer.length: "buffer=" + buffer + " bufferSize=" + bufferSize + " buffer.length=" + (buffer != null ? buffer.length : 0);
if (newSize != bufferSize) {
checkBufferSize(newSize);
bufferSize = newSize;
if (buffer != null) {
// Resize the existing buffer and carefully save as
// many bytes as possible starting from the current
// bufferPosition
byte[] newBuffer = new byte[newSize];
final int leftInBuffer = bufferLength-bufferPosition;
final int numToCopy;
if (leftInBuffer > newSize)
numToCopy = newSize;
else
numToCopy = leftInBuffer;
System.arraycopy(buffer, bufferPosition, newBuffer, 0, numToCopy);
bufferStart += bufferPosition;
bufferPosition = 0;
bufferLength = numToCopy;
newBuffer(newBuffer);
}
}
}
protected void newBuffer(byte[] newBuffer) {
// Subclasses can do something here
buffer = newBuffer;
}
/** Returns buffer size. @see #setBufferSize */
public int getBufferSize() {
return bufferSize;
}
private void checkBufferSize(int bufferSize) {
if (bufferSize <= 0)
throw new IllegalArgumentException("bufferSize must be greater than 0 (got " + bufferSize + ")");
}
@Override
public void readBytes(byte[] b, int offset, int len) throws IOException {
readBytes(b, offset, len, true);
}
@Override
public void readBytes(byte[] b, int offset, int len, boolean useBuffer) throws IOException {
if(len <= (bufferLength-bufferPosition)){
// the buffer contains enough data to satisfy this request
if(len>0) // to allow b to be null if len is 0...
System.arraycopy(buffer, bufferPosition, b, offset, len);
bufferPosition+=len;
} else {
// the buffer does not have enough data. First serve all we've got.
int available = bufferLength - bufferPosition;
if(available > 0){
System.arraycopy(buffer, bufferPosition, b, offset, available);
offset += available;
len -= available;
bufferPosition += available;
}
// and now, read the remaining 'len' bytes:
if (useBuffer && len<bufferSize){
// If the amount left to read is small enough, and
// we are allowed to use our buffer, do it in the usual
// buffered way: fill the buffer and copy from it:
refill();
if(bufferLength<len){
// Throw an exception when refill() could not read len bytes:
System.arraycopy(buffer, 0, b, offset, bufferLength);
throw new IOException("read past EOF");
} else {
System.arraycopy(buffer, 0, b, offset, len);
bufferPosition=len;
}
} else {
// The amount left to read is larger than the buffer
// or we've been asked to not use our buffer -
// there's no performance reason not to read it all
// at once. Note that unlike the previous code of
// this function, there is no need to do a seek
// here, because there's no need to reread what we
// had in the buffer.
long after = bufferStart+bufferPosition+len;
if(after > length())
throw new IOException("read past EOF");
readInternal(b, offset, len);
bufferStart = after;
bufferPosition = 0;
bufferLength = 0; // trigger refill() on read
}
}
}
private void refill() throws IOException {
long start = bufferStart + bufferPosition;
long end = start + bufferSize;
if (end > length()) // don't read past EOF
end = length();
int newLength = (int)(end - start);
if (newLength <= 0)
throw new IOException("read past EOF");
if (buffer == null) {
newBuffer(new byte[bufferSize]); // allocate buffer lazily
seekInternal(bufferStart);
}
readInternal(buffer, 0, newLength);
bufferLength = newLength;
bufferStart = start;
bufferPosition = 0;
}
/** Expert: implements buffer refill. Reads bytes from the current position
* in the input.
* @param b the array to read bytes into
* @param offset the offset in the array to start storing bytes
* @param length the number of bytes to read
*/
protected abstract void readInternal(byte[] b, int offset, int length)
throws IOException;
@Override
public long getFilePointer() { return bufferStart + bufferPosition; }
@Override
public void seek(long pos) throws IOException {
if (pos >= bufferStart && pos < (bufferStart + bufferLength))
bufferPosition = (int)(pos - bufferStart); // seek within buffer
else {
bufferStart = pos;
bufferPosition = 0;
bufferLength = 0; // trigger refill() on read()
seekInternal(pos);
}
}
/** Expert: implements seek. Sets current position in this file, where the
* next {@link #readInternal(byte[],int,int)} will occur.
* @see #readInternal(byte[],int,int)
*/
protected abstract void seekInternal(long pos) throws IOException;
@Override
public Object clone() {
BufferedIndexInput clone = (BufferedIndexInput)super.clone();
clone.buffer = null;
clone.bufferLength = 0;
clone.bufferPosition = 0;
clone.bufferStart = getFilePointer();
return clone;
}
/**
* Flushes the in-memory bufer to the given output, copying at most
* <code>numBytes</code>.
* <p>
* <b>NOTE:</b> this method does not refill the buffer, however it does
* advance the buffer position.
*
* @return the number of bytes actually flushed from the in-memory buffer.
*/
protected int flushBuffer(IndexOutput out, long numBytes) throws IOException {
int toCopy = bufferLength - bufferPosition;
if (toCopy > numBytes) {
toCopy = (int) numBytes;
}
if (toCopy > 0) {
out.writeBytes(buffer, bufferPosition, toCopy);
bufferPosition += toCopy;
}
return toCopy;
}
@Override
public void copyBytes(IndexOutput out, long numBytes) throws IOException {
assert numBytes >= 0: "numBytes=" + numBytes;
while (numBytes > 0) {
if (bufferLength == bufferPosition) {
refill();
}
numBytes -= flushBuffer(out, numBytes);
}
}
}