/**
* Returns the next object from the log, or null if none available.
*
* @return The log record, or null if EOF
* @throws IOException If there is a low-level I/O error.
*/
public Object next() throws IOException {
if (prevPos <= 0) return null;
long endOfThisRecord = prevPos;
int thisLength = nextLength;
long recordStart = prevPos - thisLength; // back up to the beginning of the next record
prevPos = recordStart - 4; // back up 4 more to read the length of the next record
if (prevPos <= 0) return null; // this record is the header
long bufferPos = fis.getBufferPos();
if (prevPos >= bufferPos) {
// nothing to do... we're within the current buffer
} else {
// Position buffer so that this record is at the end.
// For small records, this will cause subsequent calls to next() to be within the buffer.
long seekPos = endOfThisRecord - fis.getBufferSize();
seekPos =
Math.min(
seekPos,
prevPos); // seek to the start of the record if it's larger then the block size.
seekPos = Math.max(seekPos, 0);
fis.seek(seekPos);
fis.peek(); // cause buffer to be filled
}
fis.seek(prevPos);
nextLength =
fis.readInt(); // this is the length of the *next* record (i.e. closer to the beginning)
// TODO: optionally skip document data
Object o = codec.readVal(fis);
// assert fis.position() == prevPos + 4 + thisLength; // this is only true if we read all the
// data (and we currently skip reading SolrInputDocument
return o;
}
public FSReverseReader() throws IOException {
incref();
long sz;
synchronized (TransactionLog.this) {
fos.flushBuffer();
sz = fos.size();
assert sz == channel.size();
}
fis = new ChannelFastInputStream(channel, 0);
if (sz >= 4) {
// readHeader(fis); // should not be needed
prevPos = sz - 4;
fis.seek(prevPos);
nextLength = fis.readInt();
}
}